Bisaryl diphosphates such as bisphenol A bis(diphenyl)-phosphate can be effective flame retardants for polymer resins. For example, polyphenylene oxide/high-impact polystyrene ("PPO/HIPS") and polycarbonate/acrylonitrile-butediene-styrene ("PC/ABS") blends can be improved with bisaryl diphosphate flame retardants.
Because of their commercial utility, various processes for the manufacture of bisaryl diphosphates have been developed. For example, it is known that bisphenol A bis(diphenyl)-phosphate can be obtained by catalytically reacting a phosphorus oxyhalide with bisphenol A and then reacting the intermediate with phenol.
Prior art processes for making and using bisaryl diphosphates include one or more steps to remove the catalyst from the diphosphate. The most common method employed for catalyst removal has been by aqueous washing which leads to emulsions with the product. However, the residual water must generally be removed prior to use as a flame retardant.
Prior art processes for making and using bisaryl diphosphates also disclose that the triaryl phosphate content of the final products should be reduced. Accordingly, prior art processes typically employed a non-reactive solvent to reduce triaryl phosphates.
In view of the above it can be seen that a need exists for improved methods of flame retarding polymer resins with bisaryl diphosphate compounds. The present invention addresses that need.